Although large areas of the Yukon remained ice-free during the Pleistocene, the remainder of the western Canadian arctic was glaciated. Many of the deeper lakes (> 20 m) were created by glacial scour or morainal damming of mountain valleys. Kettle lakes and oxbow lakes are common in areas of low relief such as on the Mackenzie River Delta. The formation of thermokarst lakes is most active in the ice-rich soils of the arctic coastal plain. Most western arctic aquatic habitats have low conductivities, but saline lakes do occur in coastal regions.
All of the eastern arctic was glaciated during the Wisconsinan, with the exception of small areas along the north coast of Baffin Island and other high arctic islands. Glacial scours and morainal deposits have played a key role in forming deep lakes, which are largely restricted to areas of exposed bedrock. Isostatic rebound following deglaciation has also been a direct force in lake formation, as most islands and coastal regions with an elevation of less than 100 m have risen above sea level. Many of the lakes in these coastal regions were originally fjords, but have now been isolated from the ocean through rebound. Large numbers of shallow lakes have formed behind beach ridges, which were offshore bars exposed through uplift. Concentrations of suspended particulates are low, except in lakes fed by glacial tributaries. The water has little colour because terrestrial vegetation is sparse and allochthonous organic inputs are low. With the exception of a few coastal habitats, ionic concentrations are low, ranging from 10 uS/cm on granitic bedrock to 300 uS/cm on sedimentary substrates. Most lakes are oligotrophic.
Virtually all of western Canada was covered by glaciers during the Pleistocene. In mountainous regions, this led to the development of cirque lakes in basins and deep elongate lakes in what were once glacially carved valleys. The 20,000 lakes of British Columbia are distributed uniformly throughout the province. By contrast, continental glaciers scoured the three prairie provinces but the 15,000 lakes of glacial origin in Alberta, Saskatchewan, and Manitoba are restricted to the northern third of these provinces. Except for glacially impounded lakes, the lakes of the Western Plains tend to be shallow and marshy. Aquatic habitats in northern sections of the prairie provinces and those in British Columbia are typically surrounded by coniferous forests. Their waters are ordinarily dystrotrophic, (brown-water lakes with very low conductivity, low cation content and a very high humus content, often characterized by low plankton production) and suspended particle loadings are low.
In contrast to other regions of Canada, habitats show substantial variation in salinity. Lakes in the northern sections of all four provinces and those in coastal British Columbia have low conductivity. Saline habitats occur in the intermontane prairie region of British Columbia, as well as in the southern sections of the prairie provinces. Salinity levels in these habitats vary in relation to water levels.
Virtually all of eastern Canada was covered by glaciers until approximately 14 000 years ago. In areas of exposed bedrock, lakes fill basins scoured by glacial action, while in regions of glacial outwash, kettle and moraine dammed lakes dominate. Ontario and Quebec possess half of the lake habitats of Canada. Direct counts from maps have indicated the presence of 226, 918 lakes in Ontario, but there are likely at least 500, 000 lakes with a surface area greater than 1 hectare. There are at least one million lakes in Quebec and another 100, 000 lakes in the Maritime provinces. Only 64 of the lakes in Ontario have surface areas in excess of 10, 000 hectares, and 85% of these habitats range in size from 1-100 hectares.
Lakes of eastern Canada are typically surrounded by boreal or deciduous forest, and allochthonous inputs of organic matter are substantial. Lakes on the Precambrian Shield have long retention times and the water is often colored with organic materials. Suspended particle loadings are usually low and conductivities range from 100-400 uS/cm.